Minimization of channel filters within wireless access nodes

ABSTRACT

A wireless access node includes a first radio operable to transmit/receive on one of at least N transmission channels. A second radio is operable to transmit/receive on another one of the at least N transmission channels. A first filter bank, of less than N filters, filters a first transmit/receive signal of the first radio. A second filter bank, of less than N filters, filters a second transmit/receive signal of the second radio. Generally, N is greater than 2.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/820,493 filed Apr. 8, 2004 now U.S. Pat. No. 7,362,737.

FIELD OF THE INVENTION

The invention relates generally to communication networks. Moreparticularly, the invention relates to minimization of channel filterswithin wireless access nodes of a mesh network.

BACKGROUND OF THE INVENTION

Wireless access devices are becoming more prevalent. Wireless access canbe implemented in many different forms, including connecting a wirelessaccess device (client) through a wireless mesh network that providesconnection to a wired network. FIG. 1 shows a wireless mesh network thatincludes a client device 140. The wired gateway in the FIG. 1 can acceptclients directly, so it can also be an access node. The client device140 is wirelessly connected to an access node 130. The wireless accessnode 130 is wirelessly connected to a wired gateway 110 through anotherwireless access node 120. The wired gateway 110 can provide access tothe internet 100 as an access node.

The transfer of information from the client 140 to the gateway 110 isgenerally bidirectional. That is, information flows from the clientdevice 140 to the gateway 110 (generally referred to as upstreamtraffic) and information flows from the gateway 110 to the client device140 (generally referred to as downstream traffic). The amount of dataper unit time that flows between the gateway 110 and the client device140 is called throughput. The maximum amount of data that can flow perunit time is called maximum throughput. It is desirable to maximize thethroughput of wireless mesh networks.

The wireless connections 150, 160, 170 between the gateway 150, theaccess nodes 120, 130 and the client device 140, can be implemented witheither full duplex or half duplex transceivers. Full duplex transceiversare able to transmit and receive at the same time, whereas half duplexreceives can either transmit or receive at a given time. Half-duplextransceivers are typically cheaper and more easily available becausethey are less complex than full duplex transceivers.

Mesh networks such as the mesh network shown in FIG. 1 can suffer frominterference problems. For example, the access node 130 can suffer fromself-interference or interference due to transmission signals generatedby other access nodes. A first dashed line 180 shows self-interferencein which signals transmitted from access node 130 through channel 170are coupled back to the access node 130 through the channel 160. Otherinterference is shown by dashed line 190 in which the signalstransmitted from the access node 130 through the channel 170 are coupledto the access node 120 through the channel 150. This interference canreduce the maximum throughput delivered by the mesh.

Mesh networks can be constructed with omni-directional antennas to allowthe relative orientations of the access nodes and clients to change withrespect to each other. Omni-directional antennas, unlike directionalantennas, allow access nodes and clients to communicate without havingto maintain strict control over the relative locations of the accessnodes and clients. However, interference between communication channelsis more difficult to control with mesh networks that includeomni-directional antennas.

Interference between access nodes and clients can be reduced byallocating different non-overlapping frequency spectrum to differentchannels that are close in proximity. For example, a first channel 150can be allocated a first frequency spectrum channel, and a secondchannel 160 can be allocated a second frequency spectrum channel.Therefore, the interference between the first channel 150 and the secondchannel 160 can be greatly reduced. A third channel 170 can include athird frequency spectrum channel.

Actual implementations of mesh networks still suffer some interferenceeven when different frequency spectra are allocated for differenttransmission channels of the mesh network. Some signal power from onechannel will always couple into a neighboring channel because thesignals transmitted are never completely contained within the designatedchannel. That is, for example, signals transmitted over the firstchannel 150 will always include some signal power within the secondchannel 160 and the third channel 170. This undesired adjacent channelsignal power causes interference. Furthermore, even if the transmittedsignals are completely contained within their designated channels, theirrelatively high power can cause loss of sensitivity for nearbyreceivers.

Filtering can be included within radios of the access node to filtertransmitted and received signals of the radios. The filtering reducesthe effects of undesired neighboring transmission channel signals.However, the filtering can add undesired cost to the access nodes.

It is desirable to have a wireless mesh network in which the throughputof the mesh network is optimized while minimizing interference andminimizing hardware costs associated with access nodes of the wirelessmesh network.

SUMMARY OF THE INVENTION

The invention includes an apparatus and method for minimizinginterference and hardware costs of wireless access nodes.

A first embodiment of the invention includes a wireless access node. Thewireless access node includes a first radio operable to transmit/receiveon one of at least N transmission channels. A second radio is operableto transmit/receive on another one of the at least N transmissionchannels. A first filter bank, of less than N filters, filters a firsttransmit/receive signal of the first radio. A second filter bank, ofless than N filters, filters a second transmit/receive signal of thesecond radio. Generally, N is greater than 2.

Another embodiment of the invention also includes a wireless accessnode. The wireless access node includes a first radio operable totransmit/receive on one of at least N transmission channels, and asecond radio operable to transmit/receive on another one of the at leastN transmission channels, wherein N is greater than 2. In a first mode,the access node is in communication with a first device and a seconddevice, the first radio being in communication with the first device,and the second radio being in communication with the second device. In asecond mode, the communication of the access node to the first deviceand the second device is reversible so that the first radio is incommunication with the second device and the second radio is incommunication with the first device.

Another embodiment of the invention includes a wireless mesh network.The wireless mesh network includes a plurality of wireless access nodes.Each wireless access nodes is in communication with at least one otherwireless access node. Each wireless access node includes a first radiooperable to transmit/receive on one of at least N transmission channels.A second radio is operable to transmit/receive on another one of the atleast N transmission channels. A first filter bank, of less than Nfilters, filters a first transmit/receive signal of the first radio. Asecond filter bank, of less than N filters, filters a secondtransmit/receive signal of the second radio.

Another embodiment if the invention includes a method of routinginformation through at least one access node of a mesh network. Themethod includes selecting a routing path between a client and a gateway,selecting transmission channel for each hop of the selected routingpath, and selecting an upstream versus downstream orientation of the atleast one access node within the selected routing path, wherein theorientation of the at least one access node is able to rotate. Themethod can further include selecting channel filtering within the atleast one access node within the selected routing path.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, illustrating by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a network device connected to a client through a meshnetwork.

FIG. 2 shows an access node that includes channel filtering.

FIG. 3 shows an access node that includes channel filtering, and isconfigured to allow reversible transmission.

FIG. 4 shows an access node that includes channel filtering, isconfigured to allow reversible transmission, and provides isolationbetween radios within the access node.

FIGS. 5A, 5B, 5C, 5D show frequency responses of tuned filters,according to one embodiment of the invention.

FIG. 6 shows a mesh network that includes access nodes similar to theaccess node of FIG. 4.

FIG. 7 is a flow chart showing steps includes in a method of operatingan access node according to an embodiment of the invention.

DETAILED DESCRIPTION

As shown in the drawings for purposes of illustration, the invention isembodied in methods of routing within a mesh network, methods offiltering transmission signals of the access nodes, and filteringsystems within the access nodes of mesh networks.

FIG. 2 shows an access node 200 that includes channel filtering. Theaccess node 200 includes a first radio 210 and a second radio 220. Thefirst radio 210 can be dedicated to wireless communication with upstreamdevices of a mesh network, and the second radio 220 can be dedicated towireless communication with downstream devices of the mesh network. Thisembodiment of the access node 200 includes three communication channelsper radio 210, 220. Three filters 232, 234, 236 of the first radio 210provide filtering of the wireless signals at frequencies correspondingto the three communication channels associated with the first radio 210.Three other filters 242, 244, 246 provide filtering of wireless signalsat frequencies associated with the three communication channelsassociated with the second radio 220. Clearly, the number of filters canbe increased for systems that include more than three communicationchannels. The filtered signals are received and transmitted throughomni-directional antennas 270, 280. Another configuration can includeswitchable sector antennas which include many of the same pitfalls asomni-directional antennas. Operation of the first radio and the secondradio is controlled by a controller 215.

The filters 232, 234, 236, 242, 244, 246 are configured to pass signalswithin the frequency spectrum that corresponds with the communicationchannel associated with each of the filters. Signals outside of theintended frequency spectra of the filters are to be rejected, therebyreducing interference between the communication channels. The firstfilter set (F1) 232, 242 pass signals having carrier frequencies withinthe first communications channel. The second filter set (F2) 234, 244pass signals having carrier frequencies within the second communicationschannel. The third filter set (F3) 236, 246 pass signals having carrierfrequencies within the third communications channel.

As described, the filtering of the access node 200 of FIG. 2 helpsreduce interference. However, the filtering is difficult to implementdue to other problems. The switches 251, 252, 254, 255, 257, 258, 260,261 can be operationally undesirable because the switches are lossy andrequire careful impedance matching. Additionally, the six filters ofthis embodiment can be expensive. A received or transmitted signal mayhave to pass through as many as four lossy switches, which results insignal loss and lower system sensitivity. The second set of filters 234,244 must be symmetric and cannot be tailored for better rejection ofeither the upper or lower bands (F1, F3). Access nodes that include morethan three channels must include an even greater number of switches,increasing the signal loss and decreasing the system sensitivity evenmore. Clearly, the access node filter configuration of FIG. 2 is notadaptable for scaling.

FIG. 3 shows an access node 300 that includes channel filtering, and isconfigured to allow reversible transmission. The reversible transmissionallows a reduction in the number of filters. This is advantageousbecause the three channel filters of the access node 300 aresubstantially less expensive than the six channel filters of the accessnode 200 of FIG. 2.

Switches 331, 332, 333, 334, 335, 336 are controlled so that each radio310, 320 has transmitted and received signals filtered at one of threepossible communication channel frequencies. A first filter (FILTER1) 342passes signals having a carrier frequencies corresponding to a firstcommunication channel, a second filter (FILTER2) 344 passes signalshaving carrier frequencies corresponding to a second communicationchannel, and a third filter (FILTER3) passes signals having carrierfrequencies corresponding to a third communication channel. Thecommunication signals of the radios 310, 320 are received andtransmitted through omni-directional antennas 370, 380.

This reversible transmission configuration allows a reduction in thenumber of filters. However, this configuration can suffer due to a lackof isolation between the filtering switches 331,332,333,334,335,336 ofthe radios. The switches 332,333,334,335,336 route the transmissionsignals of the first radio 310 and the second radio 330 through selectedfilters 342, 344, 346. Coupling can occur between the transmissionsignals of the radios 310, 320 through the switches 332, 333, 334, 335,336 as shown, for example, by arrow 360. This coupling to some extentdefeats the purpose of filtering, which is to isolate the two radiosfrom one another. That is, the coupling can cause signals from onetransmission channel to interfere with signals of another transmissionchannel. Additionally, the second filter 344 cannot be tailored forrejection of either the frequencies of the first communication channelor the third communication channel.

Reversible Transmission

Reversible transmission can be described in the context of an accessnode within a mesh network. As previously described, an access nodewithin a mesh network includes upstream data traffic (data travelingfrom a client to a gateway) and downstream data traffic (data travelingfrom the gateway to the client). The access node 200 of FIG. 2 includesone radio 210 dedicated to upstream traffic and one radio dedicated todownstream traffic 220.

Reversible transmission, as defined here, includes each radio of anaccess node being able to handle both upstream and downstream traffic asdetermined by routing between the client and the gateway. Withomni-directional antennas, the rotation between upstream and downstreamcan be accomplished by the routing. For directional or smart antennaarrays, the rotation can be additionally accomplished by physicallyrotating the antennas, or by proper selection of antennas within anarray.

Reversible transmission allows the channel responses associated with theradios of the access nodes to be tuned or customized. For example, oneradio can be dedicated to transmission of a subset of the total numberof transmission channels, and another radio of the access nodes can bededicated to another subset of the total number transmission channels.That is, for example, if the access nodes include three transmissionchannels, one radio of each access node can be optimized fortransmission over two of the channels, and another radio can beoptimized for transmission over a different two channels. This allowseach radio to be individually optimized. The optimization can include,for example, tuning of filters, amplifiers and antennas.

Generally, an embodiment of a reversible access node includes a firstradio operable to transmit/receive on one of at least N transmissionchannels, and a second radio operable to transmit/receive on another oneof the at least N transmission channels, wherein N is greater than 2.The access node can communicate with a first device and a second device(first and second devices include gateways, clients and other accessnodes). In one mode the first radio communicates with the first device,and the second radio communicates with the second device, and in another(reverse) mode the first radio communicate with the second device andthe second radio communicate with the first device.

FIG. 4 shows an access node 400 that includes channel filtering, isconfigured to allow reversible transmission, and provides isolationbetween radios within the access node 400. Like the access node 300 ofFIG. 3, the access node 400 provides reversible transmission. However,the filtering and associated switches provide much better isolationbetween the transmission channels of a first radio 410 and a secondradio 420, than the filtering and switches of the access node of FIG. 3.A barrier 490 is shown to depict physical isolation between thecircuitry associated with the first radio 410 and the second radio 420.The transmission signals of the radios 410, 420 are transmitted andreceived through omni-directional antennas 470, 480.

The first radio 410 includes a first channel filter (FILTER1) 432, and asecond channel filter (FILTER2) 434. The second radio 420 includesanother second channel filter (FILTER2′) 436 and a third channel filter(FILTER3) 438. The filters 432, 434, 436, 438 are tuned to pass desiredsignal frequencies (that is, signals within the correspondingtransmission channel), and reject undesirable signal frequencies (thatis, signals outside of the corresponding transmission channel). The twosecond channel filters 434, 436 can be tuned to pass the same signalfrequencies, but can be individually tuned to provide greater rejectionof particular out-of-band frequencies. As previously described, if thenumber of transmission channels is greater than three, then more channelfilters can be included within the radios.

Switches 431, 433, 435, 437 control the routing of the receive andtransmit signals through the filters 432, 434, 436, 438. As will bedescribed, certain combinations of the filters 432, 434, 436, 438 of theradios 410, 420 are better than other combinations.

FIGS. 5A, 5B, 5C, 5D show examples of frequency responses of tunedfilters 432, 434, 436, 438 of FIG. 4. As shown in FIG. 5A, the frequencyresponse of the first tuned filter 432 depicts a pass band thatcorresponds with the frequency spectrum of the first transmissionchannel (F1), and provides a rejection band that includes primarily thefrequency spectrum of the second transmission channel (F2). As shown inFIG. 5B, the frequency response of the second tuned filter 434 depicts apass band that is intended to correspond with the frequency spectrum ofthe second transmission channel (F2), and provides a rejection band thatincludes primarily the frequency spectrum of the third transmissionchannel (F3).

The responses of the tuned filters are as shown due to ease ofimplementation. It is generally possible to create higher performing,lower loss filters that reject a particular band of frequencies ratherthan filters that pass a particular band of frequencies. As shown by thefrequency responses (FIGS. 5A, 5B, 5C, 5D) of the tuned filters 432,434, 436, 438, the filters are band reject filters. Proper pairing ofthe filters (pairing of complementary pairs) of each radio 410, 420provides the most desirable response. For example, the first tunedfilter 432 (response of FIG. 5A) and the second tuned filter 436(response of FIG. 5C) are complementary pairs. The first tuned filter432 rejects the frequency components of the second transmission channelthe best, while the second tuned filter 436 rejects the frequencycomponents of the first transmission channel the best. The second tunedfilter 434 (response of FIG. 5B) and the third tuned filter 438(response of FIG. 5D) are complementary pairs. The second tuned filter432 rejects the frequency components of the third transmission channelthe best, while the third tuned filter 438 rejects the frequencycomponents of the second transmission channel the best.

Operationally, interference between transmission channels can minimizedbe selecting the filtering such that the filter of the first radio isthe complement of the filter of the second radio. Again, as previouslydescribed, equivalent filtering configurations can be generated for meshnetworks that include more than three communication channels betweenaccess nodes of the mesh networks.

FIG. 6 shows a mesh network that includes access nodes similar to theaccess node of FIG. 4. The mesh network includes a first access node610, a second access node 620 and third access node 630. The firstaccess node 610 includes a first radio antenna 612 and a second radioantenna 614 associated with first and second radios of the first accessnode 610. The second access node 620 includes a first radio antenna 622and a second radio antenna 624 associated with first and second radiosof the second access node 620. The third access node 630 includes afirst radio antenna 632 and a second radio antenna 634 associated withthe first and second radios of the third access node 630. A gateway 650includes an antenna 652 and a client 640 includes an antenna 642. Aspreviously described the antennas 612, 614 622, 624, 632, 634 can beomni-directional, and the access nodes 610, 620, 630 are able to rotate.

A first selected route (FIRST ROUTE) between a client 640 and a gateway650 can include the first access node 610 and the second access node620. The link 662 between the gateway 650 and the first access node 610can be over a second of three available transmission channels, and thelink 664 between the first access node 610 and the second access node620 can be over the third of three available transmission channels. Inrelation to previous discussions, the first access node 610 selects thesecond filter (FILTER2) for the communication link between the firstaccess node 610 and the gateway 650, and the first access node 610selects the third filter (FILTER3) for the communication link betweenthe first access node 610 and the second access node 620.Correspondingly, the second access node 620 selects the first filters(FILTER1) for the communication link 664 between the second access node620 and the first access node 610.

At a later time, the quality of the links may change causing thepreferred route to include the third access node 630 between the firstaccess node 610 and the gateway 650. The new route may require a changein the channel selections between the gateway and the access nodes 610,620, 630. The new route (SECOND ROUTE) may require the first access node610 to rotate so that the other radio of the first access node 610 is incommunication with the new upstream device (the third access node 630)of the new route. For example, the communication link 666 between thethird access node 630 and the first access node may require a selectionof the third of the three available communication channels, causing aselection of the third filter by the first access node 610. Thecommunication link 664 between the first access node 610 and the secondaccess node 620 could change to the first communication channel, andselect the first filter (FILTER1) for this link. Essentially, everyroute requires the access nodes within the route to select a preferredrotation. The selected rotation (relative to upstream devices anddownstream devices) can change whenever a new route is initiated.

As shown in FIG. 6, a gateway is typically a wired device that providesa wireless access node access to a network. The gateway is a networkentity that maintains an address mapping table for each client. Theaddress mapping table generally includes a MAC-IP address mapping forthe client devices. A gateway typically services several access nodes.An access node generally includes any point of attachment of a clientwith the mesh network. The access node can be a wireless access point, awired access point, a router, a hub, a gateway, or any other networkingdevice capable of attachment to a client. A client generally can includea laptop computer, a personal digital assistant (PDA), a cell-phone, orany other device that includes as interface card adaptable for use withthe mesh network of the invention. A downlink interface is a networkinterface (logical or physical) that attaches an access node to a clientdevice. An access node can have more that one downlink interface. Allother interfaces other than downlink interfaces are termed uplinkinterfaces.

Routing Decisions

Routing decisions of the network are made to optimize the informationthroughput of the network, and to minimize interference of the network.Several different possible paths through a wireless mesh network mayexist between a wired gateway and a wireless client. The selection istypically made initially by determining which of the available pathsprovides the optimal throughput. Once the initial selection has beenmade, the channel selections between the gateway, each access nodes andthe client are generally made to minimize interference of thetransmission signals along the selected path. After the channelselections have been made, the orientation (communication with anupstream or downstream device) of the radios within each access node isselected. Finally, the filters within each of the radios are selected.

An embodiment of the mesh network includes the gateways transmittingbeacons. The beacons are received by access nodes if the access nodesare physically located with respect to a transmitting gateway so thatbeacons are successful received by the access node. Access nodes thatare able to receive a beacon, re-broadcast a corresponding beacon forreception by downstream devices (other access nodes or clients). Thispermits each access node to determine at least one path to one or moregateways.

Each access node receives beacons that provide indicators of availablerouting paths to an upstream gateway. When a gateway broadcasts abeacon, the beacon is received by all first-level access nodes. Thebeacon is used to establish a route from each access node to thegateway. First level access nodes are defined by the fact that theyreceive data directly from the gateway. The first level access nodesre-broadcast the beacon data, attaching additional path data to it. Theadditional path information indicates to the second level access nodesthat the path to the gateway includes the first level access node.

For one embodiment, the link quality of the beacon received determineswhether that beacon is rebroadcast by the system. If the quality of thebeacon is above a determined threshold, it is rebroadcast. Otherwise, itis not. For one embodiment, link quality is determined by persistence,i.e. the number of times in the last several routing cycles that theparticular beacon was received. For one embodiment, the link qualityreflects the reliability of paths to the gateway, as determined by thebeacon being available for a reasonable time. The link quality isdetermined by continuously monitoring the beacons as they are receivedin every cycle. Whenever the beacon is not received in a cycle, the linkquality associated with that path is decreased. The beacon is onlytransmitted if its link quality is sufficiently high.

For another embodiment, the depth of re-broadcast is determined for thesystem. Thus, for example, an access node may rebroadcast a beacon onlyif there are 5 or fewer hops between the access node and the gateway.For another embodiment, other link quality factors, such as trafficcongestion, battery status of upstream access nodes, thickness of thepipeline, backend (i.e. gateway) capacity, latency, or other factors maybe used to determine whether the beacon should be rebroadcast.

FIG. 7 is a flow chart showing steps included in a method of operatingan access node. A first step 710 includes determining optimal routingpaths through the access node, between client devices and gateways. Asecond step 720 includes determining the transmit/receive channelallocations within the routing paths. A third step 730 includes settingthe radio rotation within the access node for upstream and downstreamtransmission as determined by the optimal routing paths. A fourth step740 includes selecting transmission filters corresponding to thetransmit/receive allocations.

Although specific embodiments of the invention have been described andillustrated, the invention is not to be limited to the specific forms orarrangements of parts so described and illustrated. The invention islimited only by the appended claims.

1. A wireless access node comprising: a first radio operable totransmit/receive on one of at least N transmission channels; a secondradio operable to transmit/receive on another one of the at least Ntransmission channels, wherein N is greater than 2; a first filter bankof less than N filters for filtering a first transmit/receive signal ofthe first radio; and a second filter bank of at least 2 but less than Nfilters for filtering a second transmit/receive signal of the secondradio, at least one of the pass-bands of the second filter bank beingdifferent than the pass-bands of the first filter bank; wherein N isgreater than 2, and wherein the combination of the first radio and thesecond radio are operable to transmit/receive on all N transmissionchannels; wherein the access node is in communication with a firstdevice and a second device, the first radio being in communication withthe first device, and the second radio being in communication with thesecond device; and wherein the communication of the access node to thefirst device and the second device is reversible so that the first radiois in communication with the second device and the second radio is incommunication with the first device.
 2. The wireless access node ofclaim 1, wherein the access node is within a mesh network, and the firstradio is in communication with at least one of the first device and thesecond device depending upon a selected mesh network routing.
 3. Amethod of routing information through at least one access node of a meshnetwork, comprising: selecting a routing path between a client and agateway; selecting a transmission channel for each hop of the selectedrouting path; selecting an upstream versus downstream orientation of atleast one access node within the selected routing path, wherein theorientation of at least one access node is able to rotate; selectingchannel filtering within the at least one access node within theselected routing path, comprising: selecting a first filter bank of atleast 2 but less than N filters for filtering a first transmit/receivesignal of a first radio; and selecting a second filter bank of at least2 but less than N filters for filtering a second transmit/receive signalof a second radio, at least one of the pass-bands of the second filterbank being different than the pass-bands of the first filter bank;wherein N is greater than 2, and wherein the combination of the firstradio and the second radio are operable to transmit/receive on all Ntransmission channels.
 4. The method of claim 3, wherein selecting arouting path comprises determining the routing path that provides amaximal throughput.
 5. The method of claim 3, wherein selecting atransmission channel for each hop of the selected routing path comprisesselecting each transmission channel for minimizing interference.
 6. Themethod of claim 3, wherein the orientation is selected based uponfilters available to the radios within the access node.
 7. The method ofclaim 3, wherein selecting channel filtering within the at least oneaccess node within the selected routing path comprises selecting thefirst filter bank within the first radio of at least one access nodethat is complementary with the second filter bank within the secondradio of the access node.